A structure body obtained by joining, onto an optical substrate (hereinafter referred to as a lens substrate) made of a material such as glass, a layer made of a material (a resin, for example) different from the material of the lens substrate is generally called a composite optical element. Typical examples thereof include a composite optical element obtained by joining a resin layer onto a lens substrate with a surface of a spherical shape and forming a surface of the resin layer into an aspherical shape.
In the composite optical element, the resin layer is formed by curing through polymerization a resin composition on a surface of a lens substrate with an ultraviolet ray. However, there has been a problem in that since the shrinkage of the resin composition during the polymerization-curing is significant, a large distortion occurs in the resin layer and thus the resin layer separates easily from the lens substrate.
To deal with this problem, Patent Literature 1 discloses a composite optical element in which a resin layer obtained by curing through polymerization a resin composition containing aromatic epoxy(meth)acrylate is provided on a surface of a glass lens. The resin composition containing aromatic epoxy(meth)acrylate is said to have small cure shrinkage.